The S-2 was the first ALCO switcher purchased by Canadian National for operation on its Canadian lines, following an earlier delivery of 21 S-2s to the Grand Trunk Western and Central Vermont. CN bought 10 units built by ALCO in 1947 numbered 7946-7955 and renumbered 8112-8121 in 1956 (8119-8121 were transferred to GTW in 1968). In 1949 CN purchased a further 20 units built by MLW numbered 7975-7994 and later renumbered 8122-8141. All were built with Blunt trucks (designed by Mr. Blunt for ALCO and apparently very flexible so that they rode well on rough yard track), powered by a turbocharged 539 engine delivering 1000 hp. Each had a large jug-shaped stack (characteristic of a turbocharged engine) and rectangular side-mounted radiator shutter assemblies.
All CN units were retired by 1975 but some of the GTW units continued in use until 1983.